Toys designed to reach the toddler and pre-school market must be capable of producing excitement and amusement if they are to be successful. From a parental standpoint, toys for toddlers must be durable and safe, considering the relatively careless treatment they are likely to receive from small children. Further benefit is derived from toys having educational value.
One toy which has achieved long term and continuing success in the market has been a spring toy consisting of an elongate steel band wound in circular fashion to form a coil. Because the steel band is quite small in cross section, it is easily bendable and therefore the coil may be compressed into a circular cylinder or stretched to a length many times that of the cylinder, all with relatively minor application of bending force. The small band cross section further serves to minimize the damping quality in the coil, maximizing the tendency for vibrations generated in the coil to repeat themselves. These properties enable the coil, when placed at the top of a stairway or inclined plane and properly actuated, to continue movement down the stairway or inclined plane and thus appear to be walking under its own power. This provides much amusement and excitement and accounts in large part for the success of the steel coil as a toy.
There are, however, characteristics of the steel coil which make it less popular with thoughtful parents. Among these is a relatively low durability. Steel has a relatively high elastic bending modulus. In other words, more force is required to bend steel as opposed to other materials. For this reason the band which forms the steel coil must be quite small in cross section.
A further problem with steel is that as compared to other materials, the elastic limit, though high in itself, is relatively low compared to the bending modulus.
These properties inherent in steel reduce toy durability in that the band forming the steel coil must be extremely small in cross section. Because the band is small in cross section, elastic deformation is accomplished with relatively small force. However, plastic or permanent deformation is also accomplished with relatively minor application of force. Consequently small children are able to permanently deform the steel spring toy with relative ease. Once permanently deformed, the spring toy is useless as it is no longer able to expand and contract in symmetrical fashion so as to "walk" down a stairway or an inclined plane.
The steel coil poses a safety hazard. Because of the small size of the band and the ease with which it can be permanently deformed, the ends of the band can become bent outwardly from the remainder of the coil and form sharp points or edges which could seriously harm a child playing with the toy.
Moreover, the steel coil is costly and offers relatively little educational value. As the steel coil is one solid color, its appearance is not designed to add to the child's excitement and amusement when playing with the toy.
Other materials, as plastics, have been used to make coil springs and spring toys. These materials are one color and have not been used with configuration indicia coordinated with the spring structure.